Effects And Mechanism Of Sodium Percarbonate On Indigenous Bacteria And Inorganic Sulfur Cycle In Black Odorous Sediments

At present,the problem of China’s urban river pollution is serious,and the treatment of black and odorous water is a need of both national and local water ecological environmental protection,the study of black and odorous sediments is an important basis for the treatment of black and odorous water body.Sodium percarbonate（SPC）,as an oxidant,has been studied for the degradation of pollutants in soil,groundwater and industrial wastewater,but no related report has been found on the mechanism of SPC’s action in the black-odorous sediments,and the influence of SPC on microbial flora is poorly understood.Therefore,in this paper,the black and odorous sediments in urban river were taken as the research object.On the basis of exploring the influence of SPC doses on the physicochemical properties and microbial community of sediments,and compared with the characteristics of hydrogen peroxide and sodium carbonate from the perspective of the inorganic sulfur cycle,the mechanism of SPC treated in the black and odorous sediments was investiaged.The main results are as follows:（1）With a single addition,it was found that the changes of various parameters charactering the physical and chemical properties of sediments were linearly correlated with the dose of SPC.The main performances were that,with the increase of SPC dose,the redox potential of sediments could be reduced,and the pH value,the contents of soluble inorganic salt（sulfate,phosphate and nitrate）,soluble organic carbon and acid extractable heavy metal ion all showed an increasing trend,and the biological risk of heavy metal increases.But as time going on,the risk of heavy metals would gradually be declined.（2）SPC treatment significantly increased the abundance of heterotrophic bacteria with fermentation,urea hydrolysis and other chemotrophic types in the sediments,but it did not affect the dominant position of Caldisericum,Leptolinea and the gunus belong to Anaerolineaceae in the original sediments.The results were as follows:in terms of carbon utilization activity,the medium dose SPC treatment had a longer-lasting effect on the carbon utilization activity of the microbial community,and had the highest sugar utilization activity,but could inhibit the utilization activity of amine.High dose SPC treatment could reduce the diversity of carbon source utilization of the microbial community.In terms of phylogenetic classification,high-dose SPC treatment could reduce the alpha diversity of the microbial community and mainly enriched the bacteria belong to the phylum Firmicutes,the class Clostridia,and the genera Petrimonas and Proteiniclasticum,while the medium-dose SPC enriched the bacteria mainly belongs to alpha-Proteobacteria and Brevundimonas.The bacteria inhibited by SPC treatments at different doses mainly belonged to Acidobacteria,Thermophilia and Sulfuricurvum.（3）After SPC treatment,there were significant correlations between the generated soluble substances in sediments and the indigenous microbial communtiy.The mechanism of SPC treatment in the black and odorous sediment is that:through the alkaline regulation of CO₃^2-,the generated the soluble organic matter in sediments（fulminant acids and proteinoid matters）were used by the heterotrophic microorganisms and then were transfer into the small molecule organic acids（formic acid,acetic acid,lactic acid,etc.）which were used by another microbes.It illustrated that SPC could indirectly provide electron donor and electron acceptor for indigenous microorganisms to stimulate the metabolic activity of native microbial community.It is the first time to reveal the new mechanism of SPC treatment in black and odorous sediments.（4）The influence of SPC on the circulation of inorganic sulfur in black and odorous sediments was a series of biochemical reaction processes,jointly caused by the hydrolysis of Na₂CO₃ and the oxygenation of H₂O₂.It was found that the oxygenation of H₂O₂ in SPC was short,and the hydrolysis of CO₃^2-was more durable which could buffer the oxidation of H₂O₂:on the one hand,the hydrolysis of Na₂CO₃ led to the increase in pH value and the amount of DOC,and CO₃^2-/HCO₃^-.S⁰ in the sediments was decomposed into S₂O₃^2-and HS^-by alkali,and the abundance of some autotrophic sulfur respiratory bacteria were increase.At the same time,the O₂ generated by the decompose of H₂O₂,in the form of an electron donor,activated the aerobic sox pathway of the bacteria to oxidize the S₂O₃^2-to generate SO₄^2-.On the other hand,the environmental changes caused by the addition of sodium percarbonate continuely inhibited the growth of sulfate reducers（Desulfovibrio and Syntrophobacter）,which led to the decrease of the sulfate reduction rate and the significant increase of SO₄^2-.When the O₂ was completely consumed,the aerobic respiration of thiooxidative bacteria was stopped,and the assimilation sulfate reduction led to the decrease of SO₄^2-.This paper revealed the mechanism of SPC as a reagent for the remediation of black and odorous sediments,updated the understanding of the effect of SPC on microbial community and metabolic function in anaerobic environment,and provided theoretical guidance for the application of SPC in in-situ remediation of polluted environment.